The background description provided herein is for the purpose of generally presenting the context of the present invention. The subject matter discussed in the background of the invention section should not be assumed to be prior art merely as a result of its mention in the background of the invention section. Similarly, a problem mentioned in the background of the invention section or associated with the subject matter of the background of the invention section should not be assumed to have been previously recognized in the prior art.
China has a vast geographic area, and energy resources and electricity loads are distributed very unevenly. The developments of astrong smart grids of ultra-high voltages (UHV) as a backbone network frame can implement cross-regional, long-distance, high-power electric power transmissions and exchanges, and optimization of wide-range power resource distributions. An UHV grid refers to a 1000 kV AC grid or ±800 kV DC grid, which is characterized by high voltages, great power, small losses, long power transmission distances and a single circuit structure. In China, UHV projects that have been put into operation at present include the southeastern Shanxi-Nanyang-Jingmen 1000 kV UHV AC test and demonstration project, the Sichuan (Xiangjiaba)-Shanghai ±800 kV UHV DC transmission project, and the Jinping-South Jiangsu ±800 kV UHV DC transmission project.
The network loss rate is defined as system loss increment caused by power consumption or transmission of per unit increment under particular time and operation manner. The UHV integrated network loss rate can be calculated through the total loss of power (including a line loss, a transformer loss, and further including a convertor station loss for DC transmission) divided by the power-giving/outputting at the starting node/port in the system. The trading network loss is one of the main trading costs, in planning and trading settlement of UHV cross-regional electricity trading, effects of the network loss on the trading plan and settlement cost must be taken into account, it is necessary to correct or reduce the settlement power or bid price according to the size of the integrated network loss rate planned value. Thus, the method for determining the UHV integrated network loss rate planned value is scientific and reasonable directly relates to economic interests of the parties of the trading, and close attention is paid thereto by trading related parties.
At present, a theoretical calculation method of UHV AC integrated network loss rates uses a power system analysis program recognized in this field, for example, a power system analysis synthesis program (PSASP) developed by China's electricity academy, to make load flow calculation on an actual system (the load flow calculation is calculation of determining steady running state parameters of respective parts of the power system according to a given grid structure, parameter and generator, load and other elements' operating conditions), to obtain powers passing through the UHV AC line and the beginning and the end of the transformer, and then calculate theoretical values of integrated network loss rate corresponding to different transmitting powers of the UHV AC line. For high-voltage and long-distance transmission lines, power loss thereof mainly includes two parts: one is resistive loss, which is caused by heating of line resistance and is a function of line resistance, wire length and line current; the other is corona loss, which is caused by corona discharge formed by ionization of air around the wire under the action of a strong electric field and is affected by meteorological condition, conductor selection, operating voltage and other factors, where the corona loss is represented by ground conductance in a transmission line model. As line-to-ground parameters in an AC line model of a related program such as PSASP only takes shunt capacitance into account and omits ground conductance, if the integrated network loss rate is calculated directly using the result of the load flow calculation of the related program such as PSASP, actually only the resistive loss of the line is taken into account, but the corona loss of the line is not considered, the corona loss of the line at 110 kV or therebelow is very tiny and can basically be ignored, however, as the corona loss is directly proportion to the square of the voltage, the corona loss of EHV and UHV AC power transmission has been a greater value and must be considered. Therefore, the theoretical calculation value of the UHV AC integrated network loss rate obtained through the related program such as PSASP definitely has certain errors due to not considering the corona loss of the line.
The method for calculating the actual value of the UHV AC integrated network loss rate uses gateway power statistical data of a certain time period in actual project practice to calculate the integrated network loss rate, and the calculation result is more precise; however, as measurement accuracy, calculated error and other factors of a metering device, also have a certain error, and the method is calculated afterwards, in consideration of timeliness of trading settlement, the method cannot be directly applied to planning and trading settlement of UHV cross-regional electricity trading.
At present, in the planning and trading settlement of UHV cross-regional electricity trading, a method for determining a planned value of the integrated network loss rate has yet not existed, and a common method is setting a single fixed network loss rate. By taking the southeastern Shanxi-Nanyang-Jingmen 1000 kV UHV AC test and demonstration project as an example, the project starts from a transformer substation in southeastern Shanxi (Changzhi), via a transformer substation in Nanyang, Henan, and terminates at a transformer substation in Jingmen, Hubei, connects power grids in two big regions, North China and Central China, and is an important transmission channel through which the coal energy center in the northwest region transmits power to the load center in the mid-east region, and in the transaction planning and settlement process of the project, the planned value of the integrated network loss rate is uniformly set as 1.5%. Although using a fixed network loss rate is simple, the following problems still exist:
1. The UHV AC integrated network loss rate varies with the change of the UHV transmission power, and the use of a fixed value has poor accuracy. Inaccurate determination of the integrated network loss rate will directly lead to inaccurate calculation of the settlement power in the UHV trading settlement, thereby affecting fairness of the transaction. It is found by statistically analyzing historical data of the UHV AC demonstration project in the past two years that, although the UHV AC integrated network loss rate is mostly maintained between 1.4%-1.5%, the minimum network loss rate is merely 1.22%, the maximum network loss rate is up to 2.17%, and the current method that plans the network loss rate as a fixed value regardless of the size of the UHV transmission power is evidently not reasonable.
2. Scalability and extensibility are lacking. The UHV AC integrated network loss rate is closely related to the transmission power, when the UHV AC actual transmission power exceeds a historical data range of projection practice, the integrated network loss rate will vary greatly, the network loss rate cannot be corrected quickly according to the current method, and scalability and extensibility are poor. With respect to deficiencies of the use of the fixed value as the planned value of the UHV AC integrated network loss rate, it is feasible to consider, in combination with UHV AC transmission theoretical line loss calculation and actual line loss rate calculation results, using the least square method or a method of curve fitting with related software (e.g., Excel, SPSS, MATLAB) to obtain a function relation between UHV AC integrated network loss rates and transmission powers, to seek out a scientific and reasonable method for determining the planned value of the integrated network loss rate applied to UHV AC cross-regional electricity trading; as the UHV AC line network structure is relatively simple, generally, the integrated network loss rate and the transmitting power present a relationship of quadratic parabola.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.